Fingerprints refer to textures formed by uneven skin surface of fingers. The fingerprint has unique and stable texture characteristics, and is generally used as a basis for identity recognition. A fingerprint sensor is a sensor for identity recognition by using the fingerprint.
FIG. 1 is a schematic structural diagram of a conventional fingerprint sensor. The fingerprint sensor includes a covering layer 11, an adhesive 12 and a fingerprint sensor chip 13. The covering layer 11 may be made from glass, sapphire, coating or the like, and is mainly intended to protect the fingerprint sensor chip 13. The adhesive 12 is adapted for fixing the covering layer 11 to the fingerprint sensor chip. The fingerprint sensor chip 13 includes a matrix formed of thousands of pixels 14 (chip sensing units). When a finger presses the fingerprint sensor, the pixel 14 senses a fingerprint texture depth of the finger 15 thereon, and a matrix formed of fingerprint text depth data output by all the pixels 14 constitutes fingerprint texture information of the finger 15.
The protection layer (including the covering layer 11 and the adhesive 12) of the fingerprint sensor is between the finger 15 and the fingerprint sensor chip 13. Therefore, the thickness of the protection layer may affect the signal-to-noise ratio of the fingerprint texture depth data collected by the fingerprint sensor, and accordingly directly affect the fingerprint texture depth data acquired by the fingerprint sensor. If the protection layer of the fingerprint sensor is too thick or too thin, performance of the product and user experience may all be directly impacted. Therefore, the thickness of the protection layer of the fingerprint needs to be strictly controlled.
Since a frame of the fingerprint sensor is generally wrapped by a protective or decorative material, the thickness of the protection layer may not be directly measured from a side of the fingerprint sensor. A conventional method for measuring the thickness of a protection layer is to directly cutting off the fingerprint sensor and then measuring the thickness of the protection layer by using a microscope. However, the method is defective in that the fingerprint sensor needs to be destroyed for the measurement; and therefore only sample detection may be carried out during mass production, measurement may not carried out for all the fingerprint sensors, and moreover, the measurement cost is high.